1. Field of the Invention
The present invention relates generally to the field of low noise amplifiers (LNAs) used in tuners. More specifically, the present invention relates to LNAs used in the tuners of set-top boxes, cable modems, and high definition television (HDTV) devices. Tuners of this type can also be used in personal video recorders (PVRs), out-of-band (OOB) devices, analog TV, and voice over internet protocol (VOIP) devices, as well as numerous other applications.
2. Related Art
Due to the complexity and availability of entertainment program source material, multiple television tuners are included in most set-top cable boxes and cable modems. These additional features, material, and functionality cause the set-top boxes to be significantly more complex and include increased functionality. Examples of this increased functionality include the ability to watch simultaneous channels, such as the popular picture-in-picture (PIP) television viewing mode and/or the ability to watch one channel while simultaneously recording another channel using a video cassette or a personal video recorder (PVR). In traditional cable-set boxes, passive splitters with sufficient bandwidth are used to split the incoming cable signal into multiple outputs in order to drive multiple tuners to provide PIP or facilitate the viewing of one channel and the simultaneous recording of another. Unfortunately, however, the use of the passive splitters degrades the overall performance of the tuner.
For example, passive splitters are known to create insertion losses of about 6 dB, which significantly degrades the performance of the associated tuners. This level of degradation, in turn, impacts the overall system's noise figure and signal-to-noise ratio (SNR). An additional drawback of passive splitters in cable set-top boxes is that they do not permit the full use of cable signal ranges. Finally, passive splitters require extensive printed circuit board area and necessitate bulky metal configurations for electromagnetic shielding in order to minimize interference.
What is needed, therefore, is an alternative to the passive splitters currently used in cable television tuners or cable modem type applications. More specifically, what is needed is a tuner implementation that can improve upon the performance of passive splitters, such that splitting the input signal into multiple signals will not significantly degrade the overall performance of the tuner. This improved approach must facilitate the full use of the associated cable signal ranges. The improved approach must also reduce space requirements, reduce cost, and ease many of the manufacturing issues surrounding production of conventional tuners used in the aforementioned applications.
What is needed is a technique to provide autonomous automatic gain control (AGC) within the amplification modules associated with cable tuning and similar systems. Additionally, what is needed is an improved tuner with autonomous AGC that can be integrated onto a single integrated circuit (IC) and be implemented, for example, in complimentary metal-oxide semiconductor (CMOS) technology.